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International audience; In this paper the photocatalytic decolorisation and mineralisation of three orange dyes (AO10, AO12 and AO8) in neutral, alkaline and hydrolysed solutions under UV light irradiation in the presence of TiO(2) nanoparticles has been compared. The investigated photocatalyst was Millennium PC-500 TiO(2) (crystallites mean size 5-10 nm) immobilised on non-woven paper. All the experiments were performed in a circulation photochemical reactor equipped with a 15 W UV lamp emitting around 365 nm. Results indicated that complete decolorisation of 250 mL pure dye solutions with initial dye concentration of 30 mg/L could be achieved in 140 min. Photocatalytic mineralisation of the neutral, alkaline and hydrolysed dye solutions was monitored by total organic carbon (TOC) decrease and ammonium ion formation. Results indicated that the photocatalytic decolorisation and mineralisation of the dyes was less efficient with the hydrolysed and alkaline dye solutions in comparison with the neutral pure dye solutions. The amount of NH(4)(+), as N-containing mineralisation product, during UV/TiO(2) process was analysed. The electrical energy consumption for photocatalytic decolorisation of the dyes was calculated and related to the treatment costs.

The Fenton and photo-Fenton mediated degradation process of Orange II was investigated in a flow photo-reactor. The degradation was monitored as a function of the wavelength of the applied light, recirculation flow rate, amount of H2O2 and the initial concentration of Orange II. Optimization of the photo-Fenton degradation mediated by Fe-Nafion membranes indicated that an Orange II (0.25 M) solution discolored above 95% within 2.5 hours at an H2O2/Orange II ratio of 20. A concomitant mineralization of 40% of Orange II was observed after 5 h reaction. Homogeneous photo-Fenton processes were able to fully discolore Orange II within 1 hour and concomitantly fully mineralize the dye in the presence of Fe(III) (2 ppm) and an H2O2/Orange II ratio of 20. Surfactants such as linear alkylbenzene sulphonates (LAS) and K-perfluoroalkyl sulphonate (FT 800) slowed down the Orange II abatement in photo-Fenton processes.